The attached patch implements the behavior described previously, so for
example the following org

#+begin_src org
  #+CAPTION: A wide table with tabulary
  #+LABEL: tbl:wide
  #+ATTR_LaTeX: table* tabulary align=l|lp{3cm}r|l
  | 1 | 2 | 3 |
  | 4 | 5 | 6 |

  #+CAPTION: A normal table with tabularx
  #+LABEL: tbl:wide
  #+ATTR_LaTeX: table tabularx align=l|lp{3cm}r|l
  | 1 | 2 | 3 |
  | 4 | 5 | 6 |
#+end_src

exports to the following latex

#+begin_src latex
  \begin{table*}[htb]
  \caption{A wide table with tabulary} \label{tbl:wide}
  \begin{center}
  \begin{tabulary}{l|lp{3cm}r|l}
   1  &  2  &  3  \\
   4  &  5  &  6  \\
  \end{tabulary}
  \end{center}
  \end{table*}


  \begin{table}[htb]
  \caption{A normal table with tabularx} \label{tbl:wide}
  \begin{center}
  \begin{tabularx}{l|lp{3cm}r|l}
   1  &  2  &  3  \\
   4  &  5  &  6  \\
  \end{tabularx}
  \end{center}
  \end{table}
#+end_src

Does this behavior and patch look reasonable?  If I don't hear by the
end of the day I will apply this patch, I just wanted to check first on
list as the export mechanisms aren't my personal area of expertise.

Thanks -- Eric